In a conventional magnetron 100 disclosed in Patent Document 1, as shown in FIG. 6, cooling fins 105 extending from fin plates 104 that are attached at predetermined intervals to an anode tube 102 in which permanent magnets 101 are disposed at the ends thereof are evenly placed over the whole region R (in FIG. 6, the broken-line frame), thereby improving the heat dissipation efficiency of the cooling fins 105.